Cynara cardunculus as raw material for the production of binderless fiberboards:: Optimization of pretreatment and pressing conditions

Cynara cardunculus was pretreated and used to produce fiberboards without synthetic adhesives. The lignocellulosic material was steam exploded through a thermo-mechanical vapor process in a batch reactor. After pretreatment the material was dried, ground, and pressed to produce the boards. The effects of pretreatment factors and pressing conditions on the chemical and physico-mechanical properties of the fiberboards were evaluated and the conditions that optimize these properties were found. Response surface methodology based on a central composite design and multiple response optimization were used. The variables studied and their respective variation ranges were: pretreatment temperature, 160-240 degrees C; pretreatment time 2.5-12.5 min; pressing temperature, 190-230 degrees C; initial and final pressing pressures, 4-20 MPa, and initial and final pressing times, 1-9 min. Good properties were obtained at optimum conditions found (modulus of elasticity up to 5970 MPa, modulus of rupture up to 59 MPa, internal bond up to 0.8 MPa, thickness swelling as low as13.5%, and water absorption as low as 18.5%). Some of the boards fully satisfy the standard specifications although they were not produced at the optimum combination of process factors. Optimum operational conditions for producing binderless fiberboards from Cynara cardunculus that fully satisfy the European standards were found based on multiple response optimization methodology.